Cam driven actuating mechanisms in general include an arm which is driven by a cam in accordance with rotation thereof. Some mechanisms employ an attraction solenoid to attract the arm and hold it at a given position. Although it is most usual that a resilient member such as a coil spring is employed to bias the arm toward and solenoid so that the solenoid does not fail to capture the arm, some practical circumstances require employment of a resilient member which biases the arm away from the solenoid.
If the arm is biased away from the solenoid, it is only the cam profile that governs whether the arm is reliably attracted by the attraction solenoid or not. It is extremely difficult, however, to reliably effect the attraction and holding of the arm in the absence of the resilient member biasing the arm toward the solenoid, because manufacturing errors are inevitable in the cam profile or in the positional relationship between the cam and the arm.